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Dazraz

Cleaning a 8" Dob mirror ?

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Hi i have noticed that my mirror has a thin layer of dust on it and was wondering how i can clean it without taking it off completely - it still works fine and viewing is clear so should i just leave it ? 

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Hi...........unless covered in Cola and flour, Thats how bad its got to be, then you could quite easily leave it alone. These mirrors can hold a hefty layer of dust before it becomes a problem.

The temptation to leave it wont  hold you back. There are vid's on you-tube, but drop out the end collar,  complete with mirror cell ,  remove the mirror and wash in tepid water,  washing up liquid, BP Cotton wool dragged over the surface, and rinsed with BP distilled water (BP= British Pharmaceutical). Reassemble, then collimate.

Iv'e reached in with one of those compressed air cans, that did the trick, but they have propellants that could damage, so Iv'e been advised. A puffer bulb from a camera may also help if you can reach in without dropping a few hairs  off your arms onto an already dusty mirror?

Leave alone or strip it out?  :eek:

Edited by Charic
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Yes you would be surprised how much dust needs to accumulate before viewing is affected.The only way to properly clean it is to remove it so I would leave it as is,hope this helps

Jonn

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Leave it alone.

More mirrors are damaged by cleaning than by dust sitting on them. :)

Just enjoy the views ;)

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I know the feeling. You see the dust and think you just can't live with it. I remember a previous post on this subject with a picture of a big observatory mirror that was so dirty it looked like you could write your name in it!

Of course, occasions may arise when the mirror has to come out and there is plenty of good advice around on how to go about it.

In the meantime, as previous posts say, you can feel reassured.

Whatever you decide, good luck.

Jason

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Aye, + 1 for all the advice above. I've a 10" truss dob which I try to take around with me wherever I go. It usually ends up in the middle of acrid scrub lands where there's a vicious amount of dust about. As you can appreciate the mirror is pretty exposed in a truss type system and has lots of bits of dirt on top of it and this thin layer of quite thick yellow dust but the views remain spectacular. As the others have said, leave it well alone :grin:

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I agree with the sentiment expressed above...

Don't clean your primary mirror unless 'the dust layer' starts

signaling you to do otherwise...

I also want to clean mine every two weeks...

it takes b@lls to leave it alone...

trust everyone here...leave it...

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Having cleaned my mirrors several times and found no obvious improvement I agree with the above wholeheartedly, but it's always puzzled me why this should be so. I know very little about optics but what I have read suggests that telescope mirrors are figured to very tight tolerances including for surface roughness and I'd have thought that the dimensions of dust particles are not negligible in comparison and that therefore even a thin layer would cause light scatter. Obviously not so, but why?

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Just to give the other view...I have cleaned many mirrors successfully..although... I agree it does/did not improve the view...its just an OCD thing..

If you do ....the technique is to run them under running water.....swish (without touching)  the surface using cotton wool and then rinse with distilled water to avoid water marks and then dry gently with a hair dryer at arms length..

Often even after a clean there are marks so cleaning only really half eases the OCD thing anyway....

so seriously..leave it!

Mark

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